The invention concerns an arrangement for illuminating a display device with a dial and relates to display devices as are used in dashboards of motor vehicles.
Display devices of this type usually have a dial, the rear side of which is printed on in such a way as to be opaque over the entire surface area with the exception of a transmitted-light region, this transmitted-light region serving for the forming of a scale. In the case of a dial with a diameter of usually up to 110 mm, the transmitted-light region generally covers an angle of between 90xc2x0 and 220xc2x0. To illuminate evenly a relatively large transmitted-light region of this type, usually a plurality of light sources arranged in an offset manner and radiating their light directly in the direction of the rear side of the dial are used. If only a single light source is used, it is assigned a solid light guide, which is arranged on the rear side of the dial and distributes the light of the light source over the transmitted-light region. Light-emitting diodes are increasingly being used nowadays as light sources.
This prior art has several disadvantages, however. With an increasing number of light sources used, the power loss increases, and consequently so too does the thermal heating. With an increasing number of light sources, the unit price of display devices of this type also increases, because additional electrical and electronic components such as resistors, shift registers etc. are required for the operation and control of each light source. A large number of components is also accompanied moreover by a higher probability of failure for the illuminating system as a whole. Configurations of illuminating arrangements with only one light source and an associated light guide are also relatively expensive, because tool costs, material costs and assembly costs for the light guide are incurred.
In addition, a considerable outlay has to be expended in the development and production process to establish for a conventional dial a half-tone overprint that ensures even illumination of the entire dial, since the printed result of the half-tone overprint is subject to wide variations in mass production, because certain process parameters such as the ink viscosity, soiling of the print screens and the printing tolerances can adversely influence the printed result to a considerable extent. If the process parameters mentioned are not subject to constant quality control, a uniformly high level of illuminating quality cannot be ensured for display devices of this type manufactured in mass production and provided with such dials, which is then directly reflected again in the acceptance of such display devices by customers.
It is thus the object of the present invention to present an arrangement for illuminating a display device with a dial in which the outlay for achieving an evenly illuminated dial is distinctly reduced.
The object is achieved by an for illuminating a display device with a dial having the features of the first claim. The dependent claims show refinements and developments of the solution found.
The solution is distinguished an arrangement for illuminating a display device with a dial, the rear side of the dial being opaque over its entire surface area with the exception of a transmitted-light region and this transmitted-light region serving for the forming of a scale, and wherein on the rear side of the dial there is arranged a reflector shell, the shaping of which is such that the light radiated from a light-emitting diode against a reflector wall is diffusely distributed over the transmitted-light region of the dial.
A structurally very advantageous solution for this arrangement is obtained if the reflector wall is arranged perpendicularly with respect to the dial and is formed by a wall of the reflector shell, the reflector wall being of a curved design in its contour extending in the plane of the dial and said reflector wall reflecting the light radiated from the light-emitting diode against a sector-shaped portion of the bottom of the reflector shell, this portion of the bottom being of a concave design, directed toward the dial, and the light being reflected to the transmitted-light region of the dial.
A particularly inexpensive solution is obtained if the reflector shell is produced in one piece from a light, plastic and the reflective shell is designed in its size and contour such that it essentially covers only the transmitted-light region of the dial.
One particular advantage of the solution found is that, instead of the half-tone overprint that is necessary in the case of conventional arrangements and is complex to achieve, and then only by several iteration steps, the dial need only have on the rear side a white solid-area overprint, which is easy to accomplish in technical printing-process-related terms.
In addition, it is also advantageous for the illuminating system as a whole that only a single light-emitting diode has to be arranged in the reflector shell for illuminating the transmitted-light region covering the entire scale. This measure noticeably simplifies the illuminating system as a whole. At the same time, the outlay for the development of a suitable geometry of the reflector shell used here is only slightly greater than in the case of conventional display devices of the generic type.